Evaluation of the therapeutic benefit of delayed administration of erythropoietin following early hypoxic-ischemic injury in rodents

Abstract

Hypoxia-ischemia (HI) and associated brain injuries are seen in premature as well as term infants with birth complications. The resulting impairments involve deficits in many cognitive domains, including language development. Poor rapid auditory processing is hypothesized to be one possible underlying factor leading to subsequent language delays. Mild hypothermia treatment for HI injuries in term infants is widely used as an intervention but can be costly and time consuming. Data suggest that the effectiveness of hypothermia treatment following HI injury declines beyond 6 h following injury. Consequently, the availability of a therapeutic alternative without these limitations could allow doctors to treat HI-injured infants more effectively and thus reduce deleterious cognitive and language outcomes. Evidence from both human studies and animal models of neonatal HI suggests that erythropoietin (Epo), an endogenous cytokine hormone, may be a therapeutic agent that can ameliorate HI brain injury and preserve subsequent cognitive development and function. The current study sought to investigate the therapeutic effectiveness of Epo when administered immediately after HI injury, or delayed at intervals following the injury, in neonatal rodents. Rat pups received an induced HI injury on postnatal day 7, followed by an intraperitoneal injection of Epo (1,000 U/kg) immediately, 60 min, or 180 min following induction of injury. Subjects were tested on rapid auditory processing tasks in juvenile (P38-42) and adult periods (P80-85). Ventricular and cortical size was also measured from post mortem tissue. Results from the current study show a therapeutic benefit of Epo when given immediately following induction of HI injury, with diminished benefit from a 60-min-delayed injection of Epo and no protection following a 180-min-delayed injection. The current data thus show that the effectiveness of a single dose of Epo in ameliorating auditory processing deficits following HI injury decreases precipitously as treatment is delayed following injury. These data may have important implications for experimental human neonatal intervention with Epo.

Figure 1

A repeated measures ANOVA revealed a trend towards a Treatment effect (p=.085, one-tail) on silent gap detection, with HI saline animals performing worse than shams. Scores represent mean attenuated response (cued/uncued*100), and lower scores indicate better performance.

Figure 2

A repeated measures ANOVA revealed no differences in Treatment between HI Epo immediate groups and Sham groups, but did show a significant Treatment effect between HI Epo 60 minute delay and shams (p<.05), as well as significant Treatment effect between HI Epo 180 minute delay and shams (p<.01) on silent gap detection. Scores represent mean attenuated response (cued/uncued*100), and lower scores indicate better performance.

Figure 3

A repeated measures ANOVA revealed a significant overall Treatment effect between HI saline and sham groups (p<.05, one-tail) on FM sweep detection. Scores represent mean attenuated response (cued/uncued*100), and lower scores indicate better performance.

Figure 4

A repeated measures ANOVA revealed no significant differences in Treatment between HI Epo immediate and sham groups, but did reveal a trend towards a Treatment effect (p =.062) between HI Epo 60 minute delay and sham groups, and a significant Treatment effect (p <.05) between HI Epo 180 minute delay and sham groups on FM sweep detection. Scores represent mean attenuated response (cued/uncued*100), and lower scores indicate better performance.